In the intact eye of the developing rd/rd, +/+ mutant mouse, interphotoreceptor-binding protein (IRBP), which is normally located extracellularly in the interphotoreceptor matrix, remains intracellular. However, when removed from the eye and placed in short-term organ culture, retinas from these mutant mice demonstrate the capacity to synthesize and secrete IRBP normally until postnatal day 11 - 12. There may then be regulatory factors which control IRBP secretion in the intact eye. In studies of the physiological role of IRBP in the normal retina using the toad (Bufo marinus) eye-cup preparation, IRBP was shown to be capable of promoting regeneration of rhodopsin in bleached ROS. Serum albumin, however, did not promote regeneration. In addition, it was shown that 11-cis retinal was removed from the RPE by IRBP but not by serum albumin. It appears, then, that IRBP plays an active role in the vision process. In initial studies on IRBP in mouse eyes inoculated with a murine coronavirus, there was a highly significant decrease in IRBP by day 3 following inoculation. In addition, IRBP was no longer restricted to its normal location in the interphotoreceptor matrix but had diffused in the direction of the vitreous, reaching as far as the inner nuclear layer.